The answer is: cereal and milk.
Cereal and milk is heterogeneous mixture, because different samples of the substance appeared to have different proportions of the components (differences in particle size of the components).
Heterogeneous mixture is not uniform in composition.
Other examples are homogeneous mixtures with uniform composition.
For example, sweetened tea is a solution.
Solution is homogeneous mixture (the same proporties of its components throughout any given sample) composed of two or more substances.